Project summary: Palpation remains one of the simplest yet effective methods for detecting malignant breast lesions because the stiffness of breast tumors usually differs significantly from surrounding tissues. Mammography has been the main tool of breast imaging for many years, mostly to detect microcalcifications (MCs) which can be associated with breast malignancies. However, this method has limited sensitivity, especially in dense breasts. Conventional B-mode ultrasound (US) imaging has been increasingly used for breast imaging. However, this method is not sensitive to tissue stiffness. Besides, US imaging suffers from speckle artifact that masks small structures;thus, it is difficult to detect MCs with this method. Significant effort has been invested to develop improved breast imaging techniques, especially those that provide palpation-like information. Vibro-acoustography (VA) is a novel non-invasive imaging method that produces palpation-like information. Since VA uses a new and unique intrinsic characteristic of tissue, it needs to be fully investigated to compare its capabilities to the more traditional breast imaging techniques. Using an experimental VA system, we have demonstrated the capability of this method to image breast in vivo, identify lesions and MCs. In the light of the results, the next logical step is to transition to a "clinical" breast VA imaging system. Using an array transducer is an important step in translating VA from experimental stage to clinical applications using a modern electronic scanning technique with a hand-held probe. The purpose of this research is to investigate the VA system based on an array transducer for breast imaging. Here, we study breast imaging with a linear array probe in conjunctin with a clinical US scanner and evaluate its performance in identification of lesions in human breast. The combined system will have the capability of producing VA and US images with suitable resolution for breast applicaions. The goals of this research will be achieved in 4 specific Aims: (1) Develop a VA system with a linear-array probe;(2) quantify the performance of the new VA system using breast phanotms;(3) Test the performance of the system on breast tissue samples;(4) Test the system on human breast. Successful completion of this research will open the way for a new class of breast imaging tools. The combination of features offered by VA, such as sensitivity to stiffness, lack of speckle in image, and sensitivity to microcalcifications, would have a significant impact in breast cancer detection. Relevance: This research aims at developing a new tool for breast imaging. In this study we examine the effectiveness of this new method as a diagnostic tool in identification of breast lesions and breast cancer.